The document discusses civil aircraft fly-by-wire system implementations and control laws. It compares the Airbus and Boeing philosophies, noting Airbus uses 5 main computers while Boeing uses 3 primary flight computers each with 3 similar lanes. It then details the Airbus implementation on the A320, A330 and A340, describing the 7 computers, 3 hydraulic systems and normal and backup control functions. Finally, it outlines the different levels of fly-by-wire control laws including normal, alternate, direct and mechanical reversion modes.

1. CIVIL SYSTEM IMPLEMENNTATIONS
AND
FLY-BY-WIRE CONTROLS LAW
Group 5:
•Nguyễn Xuân Quỳnh
•Trương Quang Phúc
•Trần Đức Sơn
•Thái Thái Sơn
•Thái Văn Tải
•Trần Đức Quân
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2. CONTENTS
I. CIVIL SYSTEM IMPLEMENTATIONS
1. TOP-LEVEL COMPARISON
2. AIRBUS IMPLEMENTATION
I. FLY-BY-WIRE CONTROL LAW
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I. CIVIL SYSTEM IMPLEMENTATIONS
Airbus introduced a fly-by-wire system on to
the A320 family and a similar system has
been carried forward to the A330/340
• The flight control and guidance of civil transport aircraft has steadily been getting more
sophisticated in recent years.
Concorde was the first civil aircraft to
have a fly-by-wire system

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I. CIVIL SYSTEM IMPLEMENTATIONS
• Boeing’s first fly-by-wire system on the Boeing 777 was widely believed to a response to the
Airbus technology development

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I. CIVIL SYSTEM IMPLEMENTATIONS
So what is the key differences between
the Airbus and Boeing philosophies and implementations ?

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I. CIVIL SYSTEM IMPLEMENTATIONS
1. TOP-LEVEL COMPARISON
Figure 1.25 Top-level Boeing & Airbus FBW comparison
 The importance and integrity aspects of flight control lead to some form of
monitoring function to ensure the safe operation of the control loop. Also for integrity
and availability reasons, some form of redundancy is usually required

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• In the Boeing philosophy, the system
comprises three Primary Flight Computers
(PFCs), each of which has three similar
lanes with dissimilar hardware but the same
software.
• Each lane has a separate role during an
operating period and the roles are cycled
after power up.
• Voting techniques are used to detect
discrepancies or disagreements between
lanes and the comparison techniques used
vary for different types of data.
I. CIVIL SYSTEM IMPLEMENTATIONS
1. TOP-LEVEL COMPARISON

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• Communication with the four Actuator
Control Electronics (ACE) units is by
multiple A629 flight control data
buses.
• The ACE units directly drive the flight
control actuators. A separate flight
control DC system is provided to
power the flight control system.
I. CIVIL SYSTEM IMPLEMENTATIONS
1. TOP-LEVEL COMPARISON

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 The Airbus approach is shown on there
I. CIVIL SYSTEM IMPLEMENTATIONS
1. TOP-LEVEL COMPARISON
Five main computers are used:
3 Flight Control Primary Computers (FCPCs)
2 Flight Control Secondary Computers (FCSCs)
Each computer comprises command and
monitor elements with different software.
The primary and secondary computers
have different architectures and different
hardware.
Command outputs from the FCSCs to
ailerons, elevators and the rudder are for
standby use only. Power sources and
signalling lanes are segregated.

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I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
 The Anglo-French Concorde apart, Airbus was the first aircraft manufacturer in recent
years to introduce Fly-By-Wire (FBW) to civil transport aircraft. The original aircraft
to utilise FBW was the A320 and the system has been used throughout the
A319/320/321 family and more recently on the A330/340. The A320 philosophy will
be described and A330/340 system briefly compared.

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I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
A320 FBW System
• Mechanical control:
Rudder
Tailplane trim
(reversionary mode)

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I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
A320 FBW System
The aircraft has three
independent hydraulic
power systems:
•blue (B)
•green (G)
•yellow (Y)

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I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
A320 FBW System
A total of seven computers undertake the flight control computation task as follows:
• Two Elevator/Aileron Computers
(ELACs). The ELACs control the
aileron and elevator actuators
according to the notation in the
figure

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I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
A320 FBW System
• Three Spoiler/Elevator Computers
(SECs).
The SECs control all of the spoilers
and in addition provide secondary
control to the elevator actuators.
The various spoiler sections have
different functions as shown
namely:
- ground spoiler mode
- speed brake mode
- load alleviation mode
- roll augmentation

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• Two Flight Augmentation
Computers (FACs).
These provide a conventional yaw
damper function, interfacing only
with the yaw damper actuators
I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
A320 FBW System

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I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
A320 FBW System
In the very unlikely event
of the failure of all
computers it is still possible
to fly and land the aircraft –
this has been demonstrated
during certification.
In this case the Tailplane
Horizontal Actuator (THS)
and rudder sections are
controlled directly by
mechanical trim inputs –
shown as M in the diagram
– which allow pitch and
lateral control of the aircraft
to be maintained.

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I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
A330/340 FBW System
The A330/340 FBW system bears many similarities to the A320 heritage as might
expected.• The pilot’s input to the Flight
Control Primary Computers
(FCPCs) and Flight Control
Secondary Computers
(FCSCs) is by means of the
sidestick controller.

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I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
A330/340 FBW System
The A330/340 FBW system bears many similarities to the A320 heritage as might expected.
• The Flight Management
Guidance and Envelope
Computers (FMGECs)
provide autopilot pitch
commands to the FCPC.

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I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
A330/340 FBW System
The A330/340 FBW system bears many similarities to the A320 heritage as might
expected.
• The normal method of
commanding the elevator
actuators is via the FCPC
although they can be
controlled by the FCSC in a
standby mode. Three
autotrim motors may be
engaged via a clutch to drive
the mechanical input to the
THS.

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I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
A330/340 FBW System
The A330/340 FBW system bears many similarities to the A320 heritage as might
expected.
• For the pitch channel, the
FCPCs provide primary
control and the FCSCs
the backup. Pilots’ inputs are
via the rudder pedals directly
or, in the case of
rudder trim, via the FCSC to
the rudder trim motors.

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I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
A330/340 FBW System
The A330/340 FBW system bears many similarities to the A320 heritage as might
expected.
• The yaw damper function
resides within the FCPCs
rather than the separate
Flight Augmentation
Computers (FACs) used on
the A320 family. Autopilot
yaw demands are fed from
the FMGECs to the FCPCs.

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I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
A330/340 FBW System
The A330/340 FBW system bears many similarities to the A320 heritage as might
expected.
• There is a variable travel
limitation unit to limit the
travel of the rudder
input at various stages of
flight. As before, the three
hydraulic systems feed the
rudder actuators and two yaw
damper actuators as
annotated on the figure.

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The overall flight control system elements for the A330/340 are:
• Three Flight Control Primary Computers (FCPCs); the function of the FCPCs has been
described
• Two Flight Control Secondary Computers (FCSCs); similarly, the function of the
secondary computers has been explained
• Two Flight Control Data Concentrators (FCDCs); the FCDCs provide data from the
primary and secondary flight computers for indication, recording and maintenance
purposes
• Two Slat/Flap Control Computers (SFCCs); the FSCCs are each able to control the full-
span leading-edge slats and trailing-edge flaps via the hydraulically driven slat and flap
motors
I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
A330/340 FBW System

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I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
Airbus Fly-By-Wire Evolution

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I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
Airbus Fly-By-Wire Evolution
The first airbus FBW aircraft was the
A320 that was first certified in 1988.
Since then the A320 family has
expanded to include the A318, A319
and A321; the A330 and A340 aircraft
have entered service and the A380 did
so in October 2007.
In that time the number of flight
control actuators has increased with
the size of the aircraft

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I. CIVIL SYSTEM IMPLEMENTATIONS
2. AIRBUS IMPLEMENTATION
Airbus Fly-By-Wire Evolution
On the A320 family the autopilot and
FMS functions are provided by
standalone units.
On the A330/340 flight guidance is
provided by the Flight Management and
Guidance Computers (FMGCs) that
embody both autopilot and guidance
functions.
On the A380 integration has progressed
with the autopilot function being
subsumed into the FCS with the FMC as
stand-alone.

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II. FLY-BY-WIRE CONTROL LAW
The authority of each of these levels may be
summarised as follows:
 Normal laws: Provision of basic control laws
with the addition of coordination algorithms
to enhance the quality of handling and
protection to avoid the exceedance of certain
attitudes and attitude rates. Double failures
in computing, sensors or actuation power
channels will cause reversion to the
Alternate mode

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II. FLY-BY-WIRE CONTROL LAW
The authority of each of these levels may be
summarised as follows:
 Alternate laws: Provision of the basic control
laws but without many of the additional
handling enhancement features and
protection offered by the Normal mode.
Further failures cause reversion to the
Mechanical mode

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II. FLY-BY-WIRE CONTROL LAW
The authority of each of these levels may be
summarised as follows:
 Direct laws: Direct relationship from control
stick to control surface, manual trimming,
certain limitations depending upon aircraft
CG and flight control system configuration.
In certain specific cases crew intervention
may enable re-engagement of the Alternate
mode. Further failures result in reversion to
Mechanical

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II. FLY-BY-WIRE CONTROL LAW
The authority of each of these levels may be
summarised as follows:
 Mechanical reversion: Rudimentary manual
control of the aircraft using pitch trim and
rudder pedals to facilitate recovery of the
aircraft electrical system or land the aircraft
as soon as is practicable

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THE END.
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